A mate had an APS AK 74s? The one with the folding stock?
Well it had a lot of issues at first, motor cage broke somehow, gearbox kept getting clogged with paint and metal chips from where the blowback mech was connected to it as there was a lot of friction in the housing of it. It definitely was putting strain on the gearbox. Though it was an AK, the M4 series rifles have a lot less weight to shift.
He replaced the motor cage and I sorted the gearbox out and disabled the blowback for him. After that it was one of the best performing guns I've ever seen, and it was entirely stock. 300fps and the range and accuracy were mental. He stuck a PSO on it and actually fielded it as a legitimate DMR.
So if you're tech savvy, go for it. But be aware that despite the price, I wouldn't say they made particularly good beginner guns.